php-fpm configuration on nginx

Hi all,
Im tuning up the Centos vps with ispconfig and nginx for Drupal 7 site. Ispconfig is realy greate panel and all works fine. But there is one problem with configurations I cant fix myself, the site has an XML import plugin and it suppose to handle large 5-10mb documents. Currently there is such error on import:

After searching for solutions for this error I have already increased the max_execution_time but cant find how to increase max_client to check if it is the reason. Please help, what can be the reason this error?